Coupling for a tank



FIG. 1 is a perspective view side of a coupling for a tank showing my design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left side elevational view thereof;

FIG. 5 is a right side elevational view thereof; and,

FIG. 6

FIG. 7 is a bottom plan view thereof. 

The ornamental design for coupling for a tank, as shown. 